You can use the simple trick of grabbing some electrical crimp-on connector ends with eyelets. Cut off the eyelets and use the eyelets for shims. You can stack them if necessary. Or, find the right washers/shims if you can. Shim the calipers if you are only running one wheelset. If you run a couple wheelsets (and each has their own rotors, such as one race set and one heavier set...) then shim the rotors to fit one caliper location.